Regulation of microglial priming with age and the impact on neural plasticity

 描述(申请人提供)：发生退行性疾病的最大风险因素是年龄。随着世界上中位年龄的持续上升，阿尔茨海默氏症和帕金森氏症等退行性疾病的流行也随之增加。大脑老化的特征包括干细胞磨损、蛋白抑制作用丧失、线粒体功能下降和炎症。这些相互关联的表型为退行性疾病的表现和进展创造了环境。这些变化的原因和出现的顺序仍然不确定，但它们对认知功能和疾病进展的影响是明确的。神经炎症描述了促炎症细胞因子表达增加的环境；最近，这种炎症状态的原因被归因于一种被称为启动的现象。小胶质细胞是中枢神经系统的主要免疫细胞，在海马区的神经发生中起着调节作用。随着小胶质细胞年龄的增长，它们表现出对促炎的M1极化的偏爱和对诱导抗炎/组织修复M2a/b表型的因素的抵抗，这种年龄相关的变化被称为启动。小胶质细胞功能受损已被证明对神经发生和长时程增强有有害影响，这表明启动在正常认知能力下降以及退行性疾病中认知障碍的快速进展中发挥了作用。我的论文利用诸如质谱学之类的技术来研究神经源性生态位内细胞类型中与年龄相关的变化。我们最近对年轻和老年的小胶质细胞进行了蛋白质组学分析，揭示了代谢途径和肌动蛋白/细胞骨架组织的年龄相关性变化。对上游调控因素的分析预测，RICTOR和皮质酮将受到抑制。Rictor是mTORC2复合体的中心成分，是哺乳动物雷帕霉素或mTOR信号通路的一半，这是一条负责感知营养丰度的通路。皮质酮是一种哺乳动物糖皮质激素，具有很强的抗炎活性。我们发现，RICTOR被siRNA抑制的小胶质细胞模仿了启动的表型，并减弱了对糖皮质激素的反应。这些发现得到了文献的支持，即抑制mTORC2会增强巨噬细胞对内毒素的炎症反应。因此，我假设mTORC2活性的年龄依赖性变化有助于启动小胶质细胞，并且mTORC2信号是糖皮质激素活性的上游调节因子。本应用的具体目的：(I)确定mTORC2活性是否以及如何随年龄变化，这种变化如何有助于小胶质细胞的启动(Ii)确定糖皮质激素受体活性在启动的表现中的作用以及mTORC2调节这一作用的机制(Iii)检测小胶质细胞启动是否通过选择性地降低RICTOR在幼年小鼠海马区的表达，从而导致神经发生和神经可塑性的降低。

 DESCRIPTION (provided by applicant): The greatest risk factor for the development of degenerative disease is aging. As the median age in the world continues to rise along with it does the prevalence of degenerative diseases like Alzheimer's and Parkinson's. The hallmarks of the aged brain include stem cell attrition, loss of proteostasis, decreased mitochondrial function, and inflammation. These interconnected phenotypes create the environment in which degenerative diseases manifest and progress. The causes of these changes and the order in which they appear are still uncertain however their impact on cognitive function and disease progression is clear. Neuroinflammation describes an environment with an increased expression of pro-inflammatory cytokines; recently the cause of this inflammatory status has been attributed to a phenomenon known as priming. Microglia are the primary immune cell of the CNS and have diverse responsibilities such as a regulatory role in neurogenesis of the hippocampus. As microglia age they exhibit preference for the pro-inflammatory M1 polarization and a resistance to factors that induce an anti-inflammatory/tissue repair M2a/b phenotype this age dependent change is known as priming. Impaired microglial function has been shown to have deleterious effects on neurogenesis and long-term potentiation suggesting a role for priming in normal cognitive decline as well as the rapid progress of cognitive impairments that occur in degenerative diseases. My dissertation utilizes techniques such as mass spectrometry to study the age related changes that occur in cell types within the neurogenic niche. We recently performed a proteomic analysis of young and old microglia which revealed age-dependent alterations in metabolic pathways and actin/cytoskeletal organization. Analysis of upstream regulators predicted an inhibition of RICTOR and corticosterone. RICTOR is a central component in the mTORC2 complex one half of the mammalian target of rapamycin or mTOR signaling pathway, a pathway responsible for sensing nutrient abundance. Corticosterone is a mammalian glucocorticoid with powerful anti- inflammatory activity. We found that microglia where RICTOR had been inhibited with siRNA mimicked a primed phenotype and attenuated the response to glucocorticoids. These findings are supported by literature showing that mTORC2 inhibition produces an enhanced inflammatory response in macrophages to LPS. Therefore I hypothesize that age-dependent changes in mTORC2 activity contribute to the priming of microglia and that the mTORC2 signaling is an upstream regulator of glucocorticoid activity. The specific aims of this application: (i) to determine if and how mTORC2 activity is altered with age and how this alteration contributes to the priming of microglia (ii) to determine the role of glucocorticoid receptor activity in the manifestation of priming and the mechanism by which mTORC2 regulates this action (iii) to examine if microglial priming drives the reduction in neurogenesis and neural plasticity by selectively reducing RICTOR expression in the hippocampus of young mice.